I. Field of the Invention
The present invention relates generally to the field of excess flow valves used to regulate and prevent excess flow of fluid or gas therethrough. More particularly, the present invention relates to excess flow valves which prevent the flow of fluid or gas through a port if the flow rate exceeds a predetermined threshold level.
II. Description of the Related Art
The use of excess flow valves is fairly standard in the gas industry. These valves are commonly used in gas delivery systems. The valves are intended to regulate the flow of gas, vapor, or fluid therethrough by limiting the flow rate to a predetermined maximum rate. If the flow rate exceeds the predetermined rate, indicating a malfunction or dangerous condition, such as in the event of damage or rupture of a hose, pipe or fitting, the valve will shut down the flow of fluid or gas automatically to prevent excessive discharge of the fluid or gas.
Typically, a gas supply system comprises a bottle or utility gas line, or other high pressure gas source, connected directly or through a pipe, or similar gas delivery means, to a regulator unit. The regulator unit supplies the gas at a low pressure rate to its final destination--e.g. a kitchen oven. The excess flow valve is typically placed at the low-pressure end of the regulator unit. The purpose of the excess flow valve is to interrupt the gas supply should a failure occur in the pressure regulator, or in any of the connecting parts such as a hose or pipe.
A typical excess flow valve comprises a sliding poppet inside a chamber capable of closing an opening in the chamber, and preventing the flow of fluid or gas therethrough. A spring is often used to urge the poppet to its open position away from the opening. As the flow rate reaches or exceeds the maximum rate, such as the rate allowed by the size of the opening and/or spring tension, the increase in pressure differential causes the poppet to slide toward the opening, against the tension of the spring, to regulate or close the valve. The difficulty, however, of using standard excess flow valves is that they cannot be adjusted and therefore cannot be used where the fluid or gas supply pressures and threshold flow rates may vary, without changing the valve.
Certain types of externally adjustable valve systems have been used in the past to enable systems to be adjusted to different flow rates and pressures without having to substantially replace critical components each time an adjustment is made. Such adjustment capabilities are designed to alleviate the difficulty of having to replace internal components, such as the spring, or change the size of the opening, each time different flow rates and pressures are encountered. These adjustable valve systems, however, have not been altogether satisfactory, in that they are not specifically designed to provide a wide range of adjustments, nor to allow the valves to be precisely set in circumstances where sensitivity to pressure changes might be needed.
An excess flow valve having limited adjustment capability is disclosed in the Sumner et al. patent, U.S. Pat. No. 3,807,442 (the "Sumner patent"). The Sumner patent provides an excess-flow check valve comprising a poppet member and a retainer member with an external adjustment capability. The distance between the poppet member and an orifice determines the flow area for the fluid passing through the valve. By varying the flow area, the differential pressure established by the fluid flow therethrough varies inversely (i.e., as the flow area decreases, the differential pressure increases). In one embodiment, the Sumner patent employs a cam member which, upon rotation, adjusts the distance between its poppet member and an orifice. The ability to adjust said distance, however, is limited by the preselected settings provided on the cam member, i.e., lobes and flats. That is, for any given application, the shut off rate determined by the cam member might be much greater than the combined requirements of the appliances connected to the gas line, which could allow substantial dangerous flow to occur without actuation of the valve. The valve also fails to accommodate for a wide range of flow rate levels which might be needed.
Another type of externally adjustable valve referred to as a velocity fuse for a hydraulic line is shown in the Maldavs patent, U.S. Pat. No. 4,383,549 (the "Maldavs patent"). The Maldavs fuse includes a poppet valve assembly having an adjustment screw extending into an internal shielded body. The shielded body helps to divert the flow of fluid away from the poppet body so that only the poppet head is exposed to the fluid flow. The internal components of the shielded body also help to dampen the movement of the poppet so that it does not react quickly to slight changes in line pressure such as those created by short term surges. An adjustment screw used in conjunction with a dampened poppet does not normally provide much sensitivity to flow pressure changes.
In view of the limitations of the prior art, the excess flow valves disclosed in Sumner and Maldavs, and other similar valves, exhibit only a limited or crude adjustment capability. In Sumners, for example, the sensitivity of the valve depends on limited preset threshold flow rate levels, and in Maldavs, the adjustment screw moves laterally and rotates against a freely rotating poppet which makes precise adjustments difficult. These excess flow valves also fail to accommodate for a wide range of flow rate levels. Accordingly, there is a need for an excess flow valve which is sensitive to virtually any desired threshold flow rate. Moreover, the threshold flow rate for such excess flow rate valves should be easily adjustable to accommodate for a wide range of fluid or gas supply pressure.